Bits and pieces of JD's life flashes before his eyes many times on the island. When Shane fought with Abby while he struggled to stand on a chair, trying not to let his legs give out with a noose tied hungrily around his neck, waiting to suck the life from him. While he was being chased by police with guns. When he was locked up in prison and the place got shot up.
It's stupid, he realizes soon enough, but in this moment, standing before his brother, he feels safe. His brother seems to be believing what he's saying, finally accepting that JD never ever killed anyone, especially not Uncle Marty, he was just having some harmless fun.
Then JD's hearing, sensitive by many years of listening to loud hard rock music, catches the sound of a knife flicking open in the solitude of the marina's murmurs as the river swishes against the dock. "What was that?"
Henry's face is smooth, emotionless. "What was what?"
Before JD can say anything, he sees a glint of silver in his brother's hands. He blinks at the knife waiting there and whispers, "What the hell? Henry?"
Henry's face cracks into a demented, horrified kind of smile. "It... it has to be like this, JD. You know too much. Abby likes you, she wants to believe you. I can't let that happen."
"You're the killer," JD breathes, trying to get away from him. The realization is like a firm punch to the gut, leaves him gasping. "No, not you. I-- I was the mess up, you were--."
"I was the second option," he says harshly. "Your parents--" JD flinches at this, blue eyes widening as he gazes at his brother. "The Dunns adopted me," he finishes in a gentler tone, unable to be completely cruel to his baby brother-- they may not be related by blood but all his memories are as JD's brother, not Abby's and he doesn't want JD to die thinking no one loved him at some point in his life. "I'm only telling you this because you deserve to know the truth--" and it hits him anew, possibly the hardest part of all this. JD's been lied to as much as he has and if it could happen any other way, Henry would let him go but he's too smart for his own good, and Wakefield wants him dead. There's very little Henry can do, despite his every instinct screaming at him to protect his little brother.
It comes down to who he wants to save more, JD or Abby. In the end, it's easy enough to decide. "I have to save Abby, you see, JD. You're right, Wakefield is alive and I can't let him have her." He shuts his eyes for a long moment, listens to his brother's hitching, desperate breaths as he tries to slip past Henry.
It takes a split second, Henry strikes blind and feels the knife dig into his brother's abdomen as he invisioned it would a million times before. When he opens his eyes, JD is leaning against him, pained wheezes coming from his gaping open mouth. Blood stains his hands and he ponders how to explain that but right now... JD is all that matters. He holds his brother up gently with one hand while he digs the knife further in with the other, whispering. "I'm sorry, I'm so sorry."
JD's unable to stand on his own anymore but Henry wants him close as he breathes his last, to make sure he doesn't die cold and alone. He ordinarily wouldn't care but this is JD, his little brother. He can still remember him as a four year old, with bright blue eyes and a shy demeanor, hero worshipping his big brother and desperate to be just like him. "Henry," he whimpers in pain, bubbles of blood coming from his mouth and popping against Henry's collar, staining it.
"It'll be over soon, it will, it will," he soothes, pulling the knife out and not even bothering to enjoy the sick suctioning sound it makes.
"I... I... Abby," JD chokes out a sob, clinging to his brother with the last of his energy.
"I know, I know--" Henry is murmuring when he hears footsteps and freezes, horror pulsing through him. If he's seen cradling his dying brother, everything will be finished-- people will know. It can't end like this! Dammit. Henry Wakefield smashes through the last bits of Henry Dunn and pushes JD roughly back, not even bothering to watch as he falls backwards and whimpers in agony. I'm sorry, I'm sorry, he thinks, running away.
He doesn't notice the tears streaming down his face until he ventures back and finds Abby standing over JD, who stammers out that it's all about her before succumbing to the wounds. Tears are not the Wakefield way, but they are the Dunn way... it seems fitting that he'd cry one last time for his dead little brother. He will never do it again, not even for Sully or Trish. Henry Dunn disappears as the last breath of his adopted brother stutters out from bloodied lips.